On Mon, Aug 17, 2015 at 07:06:10PM -0500, Bjorn Helgaas wrote: > On Mon, Aug 17, 2015 at 5:50 PM, Jiang, Dave <dave.jiang@xxxxxxxxx> wrote: > > On Mon, 2015-08-17 at 17:30 -0500, Bjorn Helgaas wrote: > >> [+cc Mike, linux-rdma] > >> > >> On Wed, Jul 29, 2015 at 04:18:54PM -0600, Keith Busch wrote: > >> > From: Dave Jiang <dave.jiang@xxxxxxxxx> > >> > > >> > This is in perperation of un-exporting the pcie_set_mps() function > >> > symbol. A driver should not be changing the MPS as that is the > >> > responsibility of the PCI subsystem. > >> > >> Please explain the implications of removing this code. Does this > >> affect > >> performance of the device? If so, how do we get that performance > >> back? > > > > Honestly I don't know. But at the same time I think the driver > > shouldn't be touching the MPS at all. Shouldn't that be left to the > > PCIe subsystem and rely on the PCIe subsystem to set this to a sane > > value? > > Yes, I think in principle the PCI core should own this, but I also > don't want to introduce a performance regression, so I think we need > to understand whether there's a problem, and if there is, fix it. Making sure Mike is CC'd directly.. Mike: I see this has been cut and pasted to HFI1 too, I would be disappointed if HFI needs it as well. :( FWIW, I totally agree with the above. MPS/MRS and related have to do with root port capability, switches in the path and any platform bugs.. I'm not sure why a driver would ever want to mess with this, and since this code doesn't walk the bus toward the root port, it is technically wrong, right? I also find it strange that qib_pcie_caps defaults to zero which means the 'tuning' reduces the payload size to the minimums (??) > >> > /* > >> > * Now the Read Request size. > >> > * No field for max supported, but PCIe spec limits it to > >> > 4096, .. it has been a bit since I looked at this, but IIRC, MRRS is also something that should not be touched by a driver? Jason -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
